Erratum in

Abstract

The inhibition of ErbB2 by the use of human antibodies can be a valuable strategy for the treatment of breast and gastric cancer. Trastuzumab, a humanized anti-ErbB2 antibody in clinical use, is effective but can engender resistance as well as cardiotoxicity. ImmunoRNases, made up of a human anti-ErbB2 scFv and human pancreatic ribonucleases (HP-RNases), have been engineered to overcome the limits of other immunotoxins, such as immunogenicity and nonspecific toxicity. Here, we report that a novel anti-ErbB2 immunoRNase, called Erb-HPDDADD-RNase, obtained by fusing Erbicin, a human ErbB2-directed scFv, with an HP-RNase variant that resists the cytosolic inhibitor protein, binds with high affinity to a panel of ErbB2-positive gastric tumor cells and inhibits their growth more than does the parental immunoRNase, which is not resistant to the inhibitor. Moreover, Erb-HP-DDADD-RNase is endowed with antiproliferative activity for trastuzumab-resistant cancer cells both in vitro and in vivo that is more potent than that of the parental immunoRNase. Importantly, Erb-HP-DDADD-RNase does not show cardiotoxic effects in vitro on human cardiomyocytes and does not impair cardiac function in a mouse model. Thus, Erb-HP-DDADD-RNase could fulfil the therapeutic need of cancer patients ineligible for trastuzumab treatment due to primary or acquired trastuzumab resistance or to cardiac dysfunction.

Internalization of immunoRNases into tumor cells expressing different levels of ErbB2. Analysis by western blotting of lysates from SKBR3 cells (high ErbB2 expression) or JIMT-1 cells (low ErbB2 expression) untreated (control) or treated with Erb–HP-RNase or Erb–HPDDADD-RNase.

Cardiotoxic effects of Erb–HP-DDADD-RNase in vitro and in vivo. (A) Effect of Erb–HP-DDADD-RNase on the viability of human fetal cardiomyocytes (HFC) in vitro. Cells were treated for 72 h with an immunoRNase at concentrations of 50 and 100 nM, treated with doxorubicin at concentrations of 0.1 and 0.25 μM or untreated (negative control). (B–D) Effects of Erb–HP-DDADD-RNase on heart function in vivo. Relative FS, RS and EF are reported before and after the treatment of mice (n = 5) with Erb–HP-DDADD-RNase (5 × 1.2 mg kg–1 of body weight over 7 days).